1. Technical Field of the Invention
The present invention relates in general to the exchange of information between systems in a mobile telecommunications network, and in particular to the exchange of identification information for mobile stations in mobile telecommunications systems.
2. Description of Related Art
To handle large numbers of subscriber stations in a mobile telecommunications network, the network must be able to conveniently distinguish between each of the various subscriber stations. Accordingly, each mobile station has an associated unique identification number that is used to identify the particular mobile station. Under the ANSI-41 standard, for example, each mobile station is assigned a unique Mobile Identification Number (MIN). The mobile station's MIN is included in virtually all signaling messages that are sent between nodes within the network or over the air interface to identify the mobile station. A problem with use of the MIN, however, is that it is only unique within a particular numbering plan. In other words, a mobile station operating in North American might have a MIN that is identical to a different mobile station that is operating in Europe. As a result, mobile stations using only the MIN for identification cannot generally roam in areas that use a different numbering plan because of the potential for conflicts with native mobile stations that may be using identical MINs.
A second identifier that can be used is the International Mobile Station Identifier (IMSI). Unlike the MIN, the IMSI is unique internationally. Thus, a mobile station that is identified by an IMSI can roam worldwide, assuming that the mobile station is otherwise capable of operating in the particular foreign country at issue.
Until recently, the ANSI-41 standard only provided for use of the MIN to identify the mobile station in transmitted messages. As a result, mobile stations that operated in accordance with the ANSI-41 standard could not typically roam outside of North America. Pursuant to IS-751, however, ANSI-41-D now supports the use of the IMSI for mobile station identification in addition to the MIN. This additional capability impacts virtually all messages that are sent in a mobile telecommunications network because nearly every message can now contain either or both a MIN and an IMSI for each mobile station (provided the mobile station at issue is assigned both a MIN and IMSI). Thus, in the case of an InterSystemPage message, for example, or in other cases where more than one mobile switching center (MSC) is involved in routing a message, IS-751 supports use of both the MIN and the IMSI to identify the mobile station.
Although both identifiers are transported, only one of the two identifiers is actually used by the network and the mobile station at any given time. IS-751 does not provide the system with a means for identifying a particular one of the identifiers to be used. Similarly, IS-751 does not provide a means for identifying an identifier that has previously been used in communicating with the mobile station. Such information might be helpful in some situations to ensure proper system operation. There is a need, therefore, for a method and system for selecting which one of a plurality of mobile station identifiers should be used in connection with transmitted network messages or network transactions or operations relating to a mobile station.